5 posts tagged with "Introduction to Cadence"

Welcome to the latest of our regular monthly Community Spotlight updates that gives you news from in and around the Cadence community!

Please see below for a roundup of the highlights:

More Cadence How To's​

You might have noticed that we have had a few more contributions to our blog from Chris Qin. Chris has been busy sharing insights, and tips on a few important Cadence topics. The objective is to help the community with any potential problems.

Here are the latest topics:

• Bad Practices and Anti-Patterns with Cadence - Part 1

• Non-Determistic Errors, Replayers and Shadowers

Even if you have not encountered these use cases - it is good to be prepared and have a solution ready.Please take a look and let us have your feedback.

Chris is also going to take a look at the Cadence Samples to make sure they are all working and if not - he's going to re-write them so that they do!

Thanks very much Chris for all the work you are doing to help improve the project!

We have covered basic components of Cadence and how to implement a Cadence worker on local environment in previous blogs. In this blog, let's write your very first HelloWorld workflow with Cadence. I've started the Cadence backend server in background and registered a domain named test-domain. You may use the code snippet for the worker service in this blog Let's first write a activity, which takes a single string argument and print a log in the console.

func helloWorldActivity(ctx context.Context, name string) (string, error) {
	logger := activity.GetLogger(ctx)
	logger.Info("helloworld activity started")
	return "Hello " + name + "!", nil
}

In the upcoming blog series, we will delve into a discussion about common bad practices and anti-patterns related to Cadence. As diverse teams often encounter distinct business use cases, it becomes imperative to address the most frequently reported issues in Cadence workflows. To provide valuable insights and guidance, the Cadence team has meticulously compiled these common challenges based on customer feedback.

• Reusing the same workflow ID for very active/continuous running workflows

Cadence organizes workflows based on their unique IDs, using a process called partitioning. If a workflow receives a large number of updates in a short period of time or frequently starts new runs using the continueAsNew function, all these updates will be directed to the same shard. Unfortunately, the Cadence backend is not equipped to handle this concentrated workload efficiently. As a result, a situation known as a "hot shard" arises, overloading the Cadence backend and worsening the problem.

Solution: Well, the best way to avoid this is simply just design your workflow in the way such that each workflow owns a uniformly distributed workflow ID across your Cadence domain. This will make sure that Cadence backend is able to evenly distribute the traffic with proper partition on your workflowIDs.

In the previous blog, we have introduced three critical components for a Cadence application: the Cadence backend, domain, and worker. Among these, the worker service is the most crucial focus for developers as it hosts the activities and workflows of a Cadence application. In this blog, I will provide a short tutorial on how to implement a simple worker service from scratch in Go.

To finish this tutorial, there are two prerequisites you need to finish first

1. Register a Cadence domain for your worker. For this tutorial, I've already registered a domain named test-domain
2. Start the Cadence backend server in background.

To get started, let's simply use the native HTTP package built in Go to start a process listening to port 3000. You may customize the port for your worker, but the port you choose should not conflict with existing port for your Cadence backend.

package main

import (
	"fmt"
	"net/http"
)

func main(){
	fmt.Println("Cadence worker started at port 3000")
	http.ListenAndServe(":3000", nil)
}

Cadence is a powerful, scalable, and fault-tolerant workflow orchestration framework that helps developers implement and manage complex workflow tasks. In most cases, developers contribute activities and workflows directly to their codebases, and they may not have a full understanding of the components behind a running Cadence application. We receive numerous inquiries about setting up Cadence in a local environment from scratch for testing. Therefore, in this article, we will explore the components that power a Cadence cluster.

There are three critical components that are essential for any Cadence application:

1. A running Cadence backend server.
2. A registered Cadence domain.
3. A running Cadence worker that registers all workflows and activities.

Let's go over these components in more details.